Share the JavaScript based LinkedHashMap implementation between constant maps and the LinkedHashMap…

sdk/lib/_internal/compiler/js_lib/js_helper.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library _js_helper;
 
 import 'dart:_async_await_error_codes' as async_error_codes;
 
 import 'dart:_js_embedded_names' show
     GET_TYPE_FROM_NAME,
     GET_ISOLATE_TAG,
     INTERCEPTED_NAMES,
     INTERCEPTORS_BY_TAG,
     LEAF_TAGS,
     METADATA,
     DEFERRED_LIBRARY_URIS,
     DEFERRED_LIBRARY_HASHES,
     INITIALIZE_LOADED_HUNK,
     IS_HUNK_LOADED,
     IS_HUNK_INITIALIZED,
     NATIVE_SUPERCLASS_TAG_NAME;
 
 import 'dart:collection';
+
 import 'dart:_isolate_helper' show
     IsolateNatives,
     enterJsAsync,
     isWorker,
     leaveJsAsync;
 
 import 'dart:async' show
     Future,
     DeferredLoadException,
     Completer,
@@ skipping 26 matching lines @@
     JS_NULL_CLASS_NAME,
     JS_OBJECT_CLASS_NAME,
     JS_OPERATOR_AS_PREFIX,
     JS_OPERATOR_IS_PREFIX,
     JS_SIGNATURE_NAME,
     JS_STRING_CONCAT,
     RAW_DART_FUNCTION_REF;
 
 import 'dart:_interceptors';
 import 'dart:_internal' as _symbol_dev;
-import 'dart:_internal' show MappedIterable;
+import 'dart:_internal' show MappedIterable, EfficientLength;
 
 import 'dart:_native_typed_data';
 
 import 'dart:_js_names' show
     extractKeys,
     mangledNames,
     unmangleGlobalNameIfPreservedAnyways,
     unmangleAllIdentifiersIfPreservedAnyways;
 
 part 'annotations.dart';
 part 'constant_map.dart';
 part 'native_helper.dart';
 part 'regexp_helper.dart';
 part 'string_helper.dart';
 part 'js_rti.dart';
+part 'linked_hash_map.dart';
 
 /// Marks the internal map in dart2js, so that internal libraries can is-check
 /// them.
 abstract class InternalMap {
 }
 
 /// No-op method that is called to inform the compiler that preambles might
 /// be needed when executing the resulting JS file in a command-line
 /// JS engine.
 requiresPreamble() {}
@@ skipping 3776 matching lines @@
   // This is a function that will return a helper function that does the
   // iteration of the sync*.
   //
   // Each invocation should give a body with fresh state.
   final dynamic /* js function */ _outerHelper;
 
   SyncStarIterable(this._outerHelper);
 
   Iterator get iterator => new SyncStarIterator(JS('', '#()', _outerHelper));
 }